The 2009 world champion, who has yet to finish higher than fifth in nine races this year, told reporters at the Hungarian Grand Prix that he was not ruling out a return to the top of the podium before the end of the current campaign.
"We still want to win a race, and I think we still can win a race," said the Briton. "So it's not going to be a complete bad year.
"The last race for us was a good step forward and the morale is high after that race, which is good to see. Obviously we're still not going to be happy with finishing fifth or sixth, we want to be fighting for wins.
"But for us to see a definite step forward in terms of performance was very positive in Nuerburgring and here we have some more parts which should help us get close to the front.
"I don't know how we will do here in terms of where we are going to finish, but Spa is a race I am really interested and excited in for fighting for a podium and I think that has to be our aim," added the 33-year-old.
Button was fifth in China, the third race of the season, and sixth three weeks ago in Germany.
The results have been mediocre by the standards of McLaren, who ended last season with the quickest car and Button winning in Brazil.
Instead of developing that car, they decided on a complete overhaul and lost their way while others opted for the evolutionary route.
McLaren, winners of eight constructors' and 12 drivers' championships, have suffered such dips before and last completed a season without a win in 2006.
In 2004, their only win was in Belgium - the next race after Hungary and the summer break - with Kimi Raikkonen.
"The main aim is to win a grand prix this year and Spa is, at the moment, probably the best race to go and look for that," said Button.
"We understand what we should bring for that circuit in terms of aero and also we are chipping away with the car the whole time, finding things.
"It's going in the right direction and as a team maybe it's a good thing that we've had issues because you start looking at every single tiny detail and when you put it all together it can make a big difference."
Button hoped that would all contribute to making McLaren a stronger team in 2014, when a new V6 engine is introduced and the regulations undergo sweeping changes.